In the state of the art, it is known to measure the quality of an over-the-air (OTA) transmission, for instance the quality of a device under test, by taking the error vector magnitude (EVM) into account. The EVM is a quantity that is of high interest since it contains as a single value an aggregated information of the quality of the OTA transmission. In fact, the EVM is a measure used to quantify the performance of the OTA transmission since the EVM provides information regarding the deviation of an actual measured (already equalized) wave form with respect to an ideal wave form. Hence, the EVM indicates the deviations of the locations of the actual constellation points from the ideal locations due to various imperfections such as noise, phase noise, distortion and so on. So far, the error vector magnitude has been measured in a conducted fashion which means that a cable or similar is connected to the device under test for testing purposes.
However, new telecommunication standards such as 5G require to measure the error vector magnitude in a non-conducted fashion, namely over-the-air.
It is known that the error vector magnitude can be measured by taking signal portions of the signal received into account that relate to different polarizations with regard to the electric and/or magnetic field impinging on the antenna.
Since the information of at least two different polarizations is required for determining the error vector magnitude, either two single-port spectrum analyzers have to be used in the state of the art or a single two-channel spectrum analyzer has to be used. However, two-channel spectrum analyzers are currently not available for frequencies of the new radio telecommunication standard, namely the 5G telecommunication standard. Thus, two single-port spectrum analyzers correspond to the technique currently used.
The usage of two single-port spectrum analyzers, results in high costs for testing a device under test over-the-air with regard to the 5G telecommunication standard, for example the quality of the device under test with regard to the over-the-air transmission, since the spectrum analyzers are expensive that have to be used for determining the EVM.
Accordingly, there is a need for a more cost-efficient possibility to perform measurements over-the-air, in particular to measure the quality of a device under test with regard to its over-the-air characteristics.